1. Field of the Invention
The invention relates to a method and a transmitter in a telecommunication network. Specifically, the invention aims to reduce PAPR (Peak-to-Average Power Ratio) in QAM modulated signal transmission.
2. Description of the Related Art
In radio systems, a data-carrying base-band signal is modulated with the carrier wave. In PSK (Phase Shift Keying) modulation, the phase of the carrier waveform is changed depending on the symbol value in the information signal. In QAM (Quadrature Amplitude Modulation), both the phase and the amplitude are changed depending on the symbol values.
QAM is an excellent modulation method from the point of view of efficiency but suffers from high PAPR. A high PAPR will need a power amplifier with a high 1-dB compression point in order to transmit the waveform undistorted even if the average power of the signal is much lower. This will lead to an expensive solution. If the signal is clipped by the amplifier, unacceptable spectral leakage to the adjacent channels will occur.